1. Field of the Invention
The present invention relates to a method of providing fast hand-over or switching services in a wireless local area network (LAN) service, and more particularly, to a method of reducing a hand-over period in the wireless LAN by using global positioning system (GPS) information, a mobile device performing the method, and a method of switching to an optimum service mode by using the GPS information.
2. Description of the Related Art
As use of multimedia data has been increasing and networks have become wireless, users now want to receive a quality of service (QoS), which is provided in the conventional wired network, also in a wireless environment (such as a wireless LAN). Generally, QoS implements an idea that transmission rates, error rates, and other characteristics can be measured, improved, and, to some extent, guaranteed in advance through management of different data transmission, and is of particular concern for the continuous transmission of high-bandwidth information on a network. However, despite the technology development in layer 3 (L3) supporting the QoS, the development has not improved much in mobile environments that are most important in the wireless LAN. This is because a resource-contention type design is employed, basically, in an IEEE 802.11 based wireless LAN when a medium access control (MAC) protocol is designed, and a mechanism to guarantee the QoS is not included. Accordingly, it is difficult to support a fast handoff service when a mobile device travels between cells.
FIG. 1 illustrates an ordinary wireless LAN service environment, and, with reference to FIG. 1, the operation of a mobile device when it is roaming will now be explained. Referring to FIG. 1, three cells are divided as subnets X 100, Y 110, and Z 120. The subnets X 100, Y 110, and Z 120 include access points (APs) 101, 111, and 121, respectively, operating in an IEEE 802.11 wireless LAN environment. Assuming that a mobile station (MS) 102 of the subnet X 100 QoS-connected from an MS 122 in the subnet Z 120 is roaming to the subnet Y 110 and the subnet X 100 and the subnet Y 110 belong to an identical extended service set (ESS), the operation will now be explained.
As the MS 102 approaches to the subnet Y 110 by being carried by a user, the signal from the AP 101 of the subnet X 100 becomes weak. Then, the MS 102 starts channel scanning for roaming. In the case of a passive scanning mode, the MS 102 receives a beacon frame from the subnet Y 110, in the case of an active scanning mode, the MS 102 transmits a probe request to APs on each channel and an AP transmitting a stronger beacon frame or probe response is selected. In this example, the AP 111 of the subnet Y 110 is selected. The MS 102 transmits a reassociation request to the currently selected AP 111. The reassociation request is a service item defined in the IEEE 802.11 standard and is used to change a basic service set (BSS) or a current connection state in an ESS. In the reassociation request, information on the previously connected AP 101 and the MS 102 itself is included. The new AP 111 notifies the handoff of the MS 102 to the previous AP 101.
In the roaming service of the wireless LAN environment of FIG. 1, as the case of roaming from the subnet X to the subnet Y, the connection between APs providing services to the MS 102 is terminated when the hand-over is performed such that the QoS is not guaranteed. A particular problem in this process is a scanning delay time taken to search for a new AP when an MS is roaming. The scanning delay time is 300˜400 msec per channel. Thus, when the number of entire channels is 12 to 14, the scanning delay time is at least 5 seconds or more. So far, the AP 101 of the subnet X 100 cannot recognize the roaming of the MS 102. Accordingly, the AP 101 transmits QoS data continuously to the MS 102 that has been already connected to another AP 111. However, since the AP 101 cannot receive an acknowledgement (ACK) for providing data, from the MS 102, this affects the performance of the entire subnet X 100 greatly. Likewise, the MS 102 loses data provided by the subnet X 100.